Pregnant women are smoking more pot these days, according to a new Kaiser Permanente study, and as California embraces recreational marijuana in 2018, experts are concerned the trend may continue.

“It’s definitely something we see,” said Dr. Amelia McLennan, an OB-GYN at UC Davis Medical Center. “It’s usually among younger patients, but really it’s across the board. Unlike tobacco and alcohol, people don’t feel like pot is at the same level in terms of risk.”

From 2009 to 2016, marijuana use among pregnant women increased from 4.2 percent to 7.1 percent in Kaiser Permanente’s Northern California healthcare system. But the biggest jump according to the study was among those 24 and younger, especially teens. Nineteen percent of women 18 to 24, and 22 percent of teen moms screened positive for marijuana at eight weeks gestation.

Medical marijuana was legalized in California in 1996, and doctors say some patients use marijuana to self-treat the nausea and vomiting associated with pregnancy or to stimulate appetite.

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“They hear a lot of misinformation,” said Dr. Nancy Goler, an OB-GYN and author of the study. “They hear medical marijuana and think it’s safe, but there are a lot of medications that aren’t safe during pregnancy.”

According to the U.S. Centers for Disease Control and Prevention, marijuana use by pregnant women can lead to health problems in infants such as low birth weight and developmental issues.

However, since marijuana is federally prohibited, there is little research that shows how marijuana affects fetal development during pregnancy, or its effect on women and babies during breastfeeding.

A committee opinion from the American College of Obstetricians and Gynecologists said: “In the absence of such data, marijuana use is discouraged.”

“Tetrahydrocannabinol and cannabinoids (in marijuana) are known to affect how neurons migrate, and there is a lot of neuron migration as the fetus develops,” Goler said. “The brain develops through the whole pregnancy, so there is no safe window. We recommend (pregnant women) stop immediately.”

Women who participated in the study were asked to self-report their marijuana use in a survey and undergo urine testing. The study’s authors said toxicology results show higher levels of marijuana than women disclosed in the survey, indicating women were under-reporting their marijuana use. Since many studies rely on participants to report their own drug use, the study’s authors said this leaves “the scope of the problem unclear.”

The results of Kaiser Permanente’s study reflect a national trend of more pot use before and during pregnancy. According to a research letter published in the Journal of the American Medical Association, pot use before pregnancy increased 62 percent from 2002 to 2014. Marijuana use during pregnancy increased from 2.37 percent to 3.85 percent in 2014.

“You have a fetal life there, and you want to give it the greatest potential it can have, and anything that interferes with that potential is worrisome,” Goler said.

If you are 21, you can grow marijuana in California. But the rules vary by city. Here is what’s legal in Sacramento if you want to grow pot. Nick PerezThe Sacramento Bee